PROJECT SUMMARY/ABSTRACT Project Summary: The Severe Acute Respiratory Syndrome, caused by a novel coronavirus (SARS-CoV), resulted in substantial morbidity and mortality in 2002-2003. With the lack of recurrence of SARS, research efforts to develop an effective vaccine have largely halted. However, coronaviruses similar to SARS-CoV have been identified in bats and other animal populations in China, making recurrence of SARS a possibility. Thus, we believe that cessation of efforts to develop a vaccine is premature. Our goal in this proposal is to develop a safe and immunogenic live attenuated vaccine for SARS-CoV. In preliminary results, we describe what we believe is the first candidate live attenuated vaccine. This recombinant virus lacks expression of the envelope (E) protein, which results in an attenuated virus that causes no disease in either hamsters or mice transgenic for expression of the SARS-CoV receptor (human angiotensin converting enzyme, hACE2) but when used to immunize these animals, provided partial protection against challenge with wild type SARS-CoV. The central objective of this proposal is to develop novel live attenuated SARS-CoV vaccines that express mutated E protein so that they are more immunogenic than E-deleted virus but remain as safe. This objective will be achieved in the following specific aims: 1) To optimize immunogenicity of rSARS-CoV-[unreadable]E virus by mutating rather than deleting the E protein. In this aim, we will delineate different regions of the E protein responsible for its various biological activities. 2) To develop a mouse- adapted rSARS-CoV with modified E protein expression, to develop rSARS-CoV-[unreadable]E lacking expression of one or more accessory proteins and to determine the basis of enhanced protective ability of rSARS-CoV-[unreadable]E after tissue culture passage. Mouse- adapted SARS-CoV causes pulmonary disease. We will develop recombinant viruses that express mutated E protein on this background. We will also optimize the vaccine by mutating other parts of the genome. 3) To test SARS-CoV-[unreadable]E and viruses expressing mutated E as vaccine candidates. As part of this aim, immune correlates of protection will be determined. We will also introduce additional modifications to the virus to make recombination with coronaviruses in the environment unlikely.